Fluid control valves are used in a wide variety of applications to control the flow of a fluid. The fluid being controlled may comprise a gas, a liquid, or a combination thereof. In some situations, the fluid may also include suspended particulates. While fluid control valves vary widely in the specific configuration used to open and close a fluid communication path through the valve, one specific type of valve actuation is performed using a solenoid. In solenoid-actuated valves, an electric current is applied to an electromagnetic coil, with the coil typically positioned around a magnetic core. The coil generally comprises a wire that is wrapped around a plastic bobbin numerous times resulting in a plurality of so-called turns. The energized solenoid generates a magnetic field. The strength of the magnetic flux of the field is proportional to the number of turns as well as the electrical current provided to the wire.
As is well-known in the art, the magnetic flux produced by the energized coil is shaped and directed by the magnetic core and a magnetic pole piece. In some solenoid valves, the pole piece can additionally act as a physical guide for the movable armature. Because the magnetic core and the pole piece direct the magnetic flux, proper positioning of the components results in the most efficient application of the magnetic flux to the movable armature. Ideally, the magnetic core and the pole piece would be positioned in a perfectly coaxial/concentric alignment. As used herein, coaxial and concentric are used interchangeably and are intended to mean that the components being referred to share a common axis or centerline. While “perfect” concentricity may not be practical due to manufacturing tolerances, those skilled in the art can readily appreciate that the more concentric the magnetic core and pole piece are positioned, the more efficiently the magnetic flux can be applied to the movable armature. Additionally, in situations where the pole piece acts as a guide tube for the movable armature, improving concentricity can improve the direction of movement of the movable armature with respect to the magnetic core.
The solenoid's efficiency can be further improved by reducing the air-gap that is made between the movable armature and the pole piece. In situations where the pole piece acts as a guide tube for the movable armature, the air-gap can be decreased by improving the concentricity between the pole piece and the magnetic core. One reason is that as the concentricity between the pole piece and the magnetic core improves, the allowable tolerance between the movable armature and the portion of the magnetic core that receives a portion of the movable armature can decrease, i.e., a larger gap is not necessary to account for a variation away from coaxial alignment.
In some solenoids, a portion of the movable armature is received in a depression formed in the magnetic core. The solenoid's efficiency can be further improved by reducing the air-gap that is made between the movable armature and the walls of the depression. Additionally, the solenoid's efficiency can be further improved by altering the external walls of the depression to adjust the magnetic force versus displacement curves experienced when the solenoid is actuated.
In addition, there is generally a desire to reduce the number of components required to manufacture the valve. One potential reduction of parts is in the seals required to prevent fluid controlled by the valve from reaching the electromagnetic coil.
As a result of the above-mentioned efficiency issues, there have been numerous prior art attempts at increasing the concentricity, decreasing the air-gap, and reducing the number of seals required.
FIG. 1 is a cross-sectional view of a portion of a prior art solenoid valve 10. The prior art solenoid valve 10 is shown and described in greater detail in U.S. Patent Application Publication 2009/0134348. The prior art solenoid valve 10 includes a wire 1 wrapped around a plastic bobbin 2 to form an electromagnetic coil. The prior art solenoid valve 10 further includes a stationary magnetic core 3 and a pole piece 4. The magnetic core 3 and pole piece 4 are inserted into the bobbin 2 and held in place with a plurality of teeth 5 and 6 formed on the core 3 and the pole piece 4, respectively. The teeth 5, 6 partially deform the plastic bobbin 2 upon insertion and prevent the core 3 and pole piece 4 from being easily removed.
Although the prior art solenoid valve 10 eliminates the need for an O-ring to create a fluid-tight seal between the pole piece 4 and the bobbin 2, the prior art solenoid valve 10 is subject to a loss of concentricity between the magnetic core 3 and the pole piece 4, and thus, a movable armature (not shown). This is shown by the longitudinal axis X-X of the magnetic core 3 being offset from the longitudinal axis Y-Y of the pole piece 4. One reason for the unintended offset is that the core 3 and the pole piece 4 are forced into the bobbin 2. Even small variances between the longitudinal axis X-X and the longitudinal axis Y-Y can reduce the magnetic flux aligned to act on the movable armature. The unaligned magnetic flux lowers the efficiency of the valve due to a lower amount of the magnetic flux acting on the movable armature in the direction of the armature's movement. Further, with a portion of the magnetic flux potentially pulling the movable armature at an angle with respect to the armature's movement, frictional forces may increase as the movable armature moves within the pole piece 4.
Furthermore, because concentricity between the magnetic core 3 and the pole piece 4 is compromised, a larger area must be formed in the magnetic core 3 to accommodate the movable armature or a smaller armature needs to be used in order to avoid the movable armature hitting the magnetic core 3. Either case results in a larger air-gap than desired.
FIG. 2 shows a cross-sectional view of another prior art valve 20. The prior art valve 20 includes a housing 21, a wire 22 wrapped around a bobbin 23 to form an electromagnetic coil, a magnetic core 24, a pole piece 25, and a movable armature 26. The prior art valve 20 improves upon the prior art valve 10 by eliminating the need to force the core 24 and pole piece 25 into the bobbin 23 using teeth or other clamping members. Rather, the prior art valve 20 utilizes a weld joint 27 to join the magnetic core 24 and the pole piece 25. The bobbin 23 is then placed over the welded components.
Although the weld joint 27 can improve upon the concentricity between the magnetic core 24 and the pole piece 25, the welding operation can be expensive and time-consuming. Further, in order to provide a suitably small air-gap between the movable armature 26 and the pole piece 25, the weld joint may be required to be ground down to provide a smooth surface, further increasing the time and cost of the assembly.
Therefore, there exists a need in the art for an improved solenoid with an improved concentricity, air-gap, and strength. The solenoid may be incorporated into a valve, an electromagnet, etc. The embodiments described below provide these and other improvements and an advance in the art is achieved. The embodiments described below provide a solenoid with an over-molded component used to hold the magnetic core and the pole piece in place. In some embodiments, the over-molded component comprises a bobbin. The over-molded component is capable of increased manufacturing tolerances that minimize the air-gap between the movable armature and the pole piece, for example.